[PATCH 3/5] dma-buf: lock the reservation object during (un)map_dma_buf

[Christian König]

First step towards unpinned DMA buf operation.

I've checked the DRM drivers to potential locking of the reservation
object, but essentially we need to audit all implementations of the
dma_buf _ops for this to work.

Signed-off-by: Christian König <christian.koenig at amd.com>
---
 drivers/dma-buf/dma-buf.c | 4 ++++
 include/linux/dma-buf.h   | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index e4c657d9fad7..4f0708cb58a7 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -631,7 +631,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
 	if (WARN_ON(!attach || !attach->dmabuf))
 		return ERR_PTR(-EINVAL);
 
+	reservation_object_lock(attach->dmabuf->resv, NULL);
 	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
+	reservation_object_unlock(attach->dmabuf->resv);
 	if (!sg_table)
 		sg_table = ERR_PTR(-ENOMEM);
 
@@ -658,8 +660,10 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
 	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
 		return;
 
+	reservation_object_lock(attach->dmabuf->resv, NULL);
 	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
 						direction);
+	reservation_object_unlock(attach->dmabuf->resv);
 }
 EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
 
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index d17cadd76802..d2ba7a027a78 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -118,6 +118,8 @@ struct dma_buf_ops {
 	 * any other kind of sharing that the exporter might wish to make
 	 * available to buffer-users.
 	 *
+	 * This is called with the dmabuf->resv object locked.
+	 *
 	 * Returns:
 	 *
 	 * A &sg_table scatter list of or the backing storage of the DMA buffer,
@@ -138,6 +140,8 @@ struct dma_buf_ops {
 	 * It should also unpin the backing storage if this is the last mapping
 	 * of the DMA buffer, it the exporter supports backing storage
 	 * migration.
+	 *
+	 * This is called with the dmabuf->resv object locked.
 	 */
 	void (*unmap_dma_buf)(struct dma_buf_attachment *,
 			      struct sg_table *,
-- 
2.14.1